JILA, National Institute of Standards and Technology, Boulder, CO, USA.
Department of Physics, University of Colorado, Boulder, CO, USA.
Nature. 2020 Dec;588(7837):239-243. doi: 10.1038/s41586-020-2980-7. Epub 2020 Dec 9.
The control of molecules is key to the investigation of quantum phases, in which rich degrees of freedom can be used to encode information and strong interactions can be precisely tuned. Inelastic losses in molecular collisions, however, have greatly hampered the engineering of low-entropy molecular systems. So far, the only quantum degenerate gas of molecules has been created via association of two highly degenerate atomic gases. Here we use an external electric field along with optical lattice confinement to create a two-dimensional Fermi gas of spin-polarized potassium-rubidium (KRb) polar molecules, in which elastic, tunable dipolar interactions dominate over all inelastic processes. Direct thermalization among the molecules in the trap leads to efficient dipolar evaporative cooling, yielding a rapid increase in phase-space density. At the onset of quantum degeneracy, we observe the effects of Fermi statistics on the thermodynamics of the molecular gas. These results demonstrate a general strategy for achieving quantum degeneracy in dipolar molecular gases in which strong, long-range and anisotropic dipolar interactions can drive the emergence of exotic many-body phases, such as interlayer pairing and p-wave superfluidity.
分子的控制是研究量子相的关键，在量子相中，可以利用丰富的自由度来编码信息，并能精确调节强相互作用。然而，分子碰撞中的非弹性损耗极大地阻碍了低熵分子系统的工程设计。到目前为止，人们仅通过两个高度简并的原子气体的缔合来创建量子简并分子气体。在这里，我们使用外加电场和光晶格限制来创建二维极化钾-铷（KRb）极性分子费米气体，其中弹性、可调谐偶极相互作用主导所有非弹性过程。阱中分子之间的直接热化导致有效的偶极蒸发冷却，从而使相空间密度迅速增加。在量子简并开始时，我们观察到费米统计对分子气体热力学的影响。这些结果展示了一种实现强、长程和各向异性偶极相互作用驱动奇异多体相（如层间配对和 p 波超流）出现的一般策略。
